1. Field of the Invention
This invention relates to an optical fiber component characteristics measuring apparatus for measuring characteristics of optical fiber components which are used in transmission control of optical signals and optical signal processing in the fields of optical transmission and optical communication techniques.
2. Related Background Art
As techniques of optical transmission and optical communication, such as the so-called ISDN have been developed, various optical fiber components for use in transmission control of optical signals containing information and processing of optical signals have been studied and developed. Such optical fiber components include for example optical fiber couplers and optical fiber filters.
One of the former optical fiber couplers comprises one or at least two optical fibers on the input side, and one or at least two optical fibers on the output side, which are connected to each other. Such optical coupler having one optical fiber on the output side performs the functions of separating only a component of a light beam incident on the optical fiber on the input side, which (component) corresponds to a spectral characteristic of the output optical fiber, and propagating the component. One of the optical couplers having at least two optical fibers on the output side has a function of dividing a light beam incident on an optical fiber on the input side into components having corresponding spectral characteristics of the output optical fibers to output or propagate the components from or through the corresponding output optical fibers. Specifically in an optical fiber coupler having one input optical fiber and a first output optical fiber of a 1300 nm-spectral characteristic and a second optical fiber of a 1550 nm spectral optical fiber (which is called 1.times.2 optical fiber coupler), when a mixed beam of a 1300 nm-wavelength and a 1550 nm-wavelength is incident on the input optical fiber, the 1300 nm-wavelength light beam and the 1550 nm-wavelength light beam are divided in accordance with their spectral characteristics to be outputted from or propagated through the corresponding output optical fibers.
The optical couplers can propagate a specific-wavelength light beam of a mixed light beam of a plurality of wavelengths, and can divide a mixed light beam into light beams of respective wavelengths. The optical couplers exert good functions which facilitate selections, expansions, etc. of communication networks of optical communication systems. Studies and developments are being made on improvement of separation characteristics of respective wavelengths, and improvement of qualities for better division characteristics and prevention of crosstalks. Also known is an optical coupler which comprises a plurality of optical fibers on the output side which have the same spectral characteristics, so that a light beam incident on an optical fiber on the input side is divided by a uniform division ratio to the respective output optical fibers. Studies and developments also being made on improvement of uniformity of division ratios.
In the last-described optical fiber coupler, optical fibers are used as optical filters so that the passage of light beams of unnecessary wavelengths are prohibited from admitting light beams of necessary wavelengths. Specifically, an optical fiber filter for passing light beams of a 1550 nm-wavelength does not pass light beams of other wavelengths, e.g. , a 1300 nm-wavelength. When a mixed light beam of a 1550 nm-wavelength and a 1300 nm-wavelength is incident, the light beam of a 1550 nm-wavelength is admitted. Thus, the optical fiber filter passes light beams of necessary wavelengths and does not pass light beams of unnecessary wavelengths. Studies and developments are being made on optical fiber filters having the so-called transmission/cuttoff characteristics improved.
Thus, optical fiber components for controlling light beams have been studied and developed with optical techniques. To further advance studies and developments of innovational and superior optical fiber components, an optical fiber components characteristics measuring apparatus for measuring characteristics of optical fiber components is essential.
A conventional optical fiber characteristics measuring apparatus of the structure of FIG. 7 is known. This device is for measuring spectral characteristics of an optical coupler (1.times.2 optical fiber coupler) 5 having one optical fiber 5a on the input side, and two optical fibers 5b, 5c having different spectral characteristics on the output side. The apparatus comprises an input mechanism for applying light to the optical fiber coupler to be measured, and an output mechanism for receiving light beams outputted from the optical fiber coupler 5 for various analyses.
The input mechanism comprises a light source 1 provided by a halogen lamp for emitting light having a flat spectral characteristic over a wide wavelength range, a chopper mechanism 2 for passing or interrupting the light, a spectroscope 3 for spectroscoping the light passing the chopper mechanism 2, and controller 4 for sweeping wavelengths of the spectroscope 3. The light from the spectroscope 3 is incident on the input optical fiber 5a through an optical connector.
The output mechanism comprises a first germanium photodiode 6 and a second germanium photodiode 7 which respectively detect the light from the output optical fiber 5b and the output optical fiber 5c, and photoelectrically generate electric signals proportional to intensities of the detected light, and lockin amplifiers 8, 9 which respectively amplify the electric signals from the photodiodes 6, 7, and an A/D converter 11 which receives the amplified electric signals through a selector circuit 10, and converts them into digital data to supply the digital data to a signal analyzing circuit 12, such as a computer.
When an operator inserts an optical fiber coupler to be measured between the input mechanism and the output mechanism and starts the measurement, light from the light source 1 is interrupted by the chopper mechanism 2 to be applied to the spectroscope 3. The light diffracted into respective wavelengths by the spectroscope 3 is separated into light of the respective wavelengths by mechanical sweep of the controller 4 to be incident on the input optical fiber 5a of the optical fiber coupler 5 to be measured. The light of the respective wavelengths which has passed through the output optical fibers 5b, 5c is photoelectrically converted by the photodiodes 6, 7 and electric signals S1, S2 proportional to intensities of the transmitted light of the respective wavelengths. The respective electric signals S1, S2 are amplified and sample-held by the lockin amplifiers 8, 9, then are delayed from each other by the selector 10 to be supplied to the A/D converter 11. Thus, digital data D1 corresponding to the electric signal S1, and digital data D2 corresponding to the electric signal S2 are supplied to the signal processing circuit 12 in a time series. A reference signal frequency of the lockin amplifiers 8, 9 are synchronous with an interrupted repeated frequency of the chopper mechanism 2. Light of a different wavelength is incident by the mechanical sweep of the controller 4 from the spectroscope 3 on the input optical fiber 5a at each chopping cycle, and the digital data D1, D2 of the respective wavelengths are supplied to the signal processing circuit 12. Respective spectral characteristics on the output optical fibers 5b, 5c are available as digital data. These digital data D1, D2 are subjected to signal processing, or displayed on a monitor television, whereby measured results of the respective spectral characteristics on the output optical fibers 5b, 5c are presented to the operator.
But in such conventional optical fiber component characteristics measuring apparatus, a spectrum generated in the spectroscope 3 is mechanically swept by the controller 4 to sequentially separate light of respective wavelengths. The mechanical sweep mechanically wears the controller 4 after a long time of use, and its reproducibility of wavelengths is lowered, with the result that wavelengths incident on optical fiber components are deflected and spectral characteristics of the optical fiber components cannot be measured with high precision. This has been a problem of the conventional optical fiber component characteristics measuring apparatus.
The sweeps of the controller 4, which are mechanically conducted, are slow, with the result that it takes a long time to provide spectral characteristics of all wavelengths of an optical fiber component to be measured. Thus another problem is that a measuring operation takes a long period of time.
A halogen lamp, which has a substantially flat. spectral characteristic in the required infrared range, is used as the light source 1. But the halogen lamp has low radiation intensities, and output light of an optical fiber component 5 to be measured is weak. A further problem is that the measuring precision on the output mechanism is low.